1. Field of the Invention
The present invention relates to structural vehicle parts manufactured by friction stir welding several parts together including extrusions that are combined to form larger structural body parts.
2. Background Art
In an effort to improve fuel economy by reducing vehicle weight, vehicle manufacturers have increasingly turned to aluminum parts. Aluminum parts may be made from aluminum sheets that are fabricated by conventional sheet metal forming and assembly processes. Aluminum extrusions are generally used to form smaller cross-section bars and reinforcements. The size of aluminum extrusions is limited due to problems associated with larger cross-section extruded aluminum parts.
It has not previously been economically feasible to form large structural components such as center tunnel and rocker beams using an extrusion process. For example, it has not been cost effective to make a center tunnel measuring 12 inches on a side or rocker beam having a cross-section including a dimension of 8 to 10 inches solely by an aluminum extrusion process.
The center tunnel of a vehicle may be used to house a gasoline tank or other fuel system components that require the tunnel to be sealed. If the tunnel is manufactured in sections, a continuous weld must be made to assure sealing. Prior art MIG or TIG welding operations must be performed intermittently due to the high heat developed that may cause substantial distortion of the panels to be joined. Panels must be MIG or TIG welded in spaced stitches on a first pass and then MIG or TIG welded on a second pass after allowing the panels to cool to connect the spaced stitches of the first pass to form an acceptable continuous MIG or TIG weld.
Another disadvantage associated with MIG or TIG welding is that both require filler metal to form a weld. Filler metal adds to the cost and weight of finished parts.
These and other problems associated with prior art structural component parts and manufacturing processes are addressed by applicants' invention as summarized below.